Conventionally, there is a detection system for detecting a packet discard between a node that makes a survey (hereinafter, referred to as a surveying node) and a node to be surveyed (hereinafter, referred to as a survey target node). This detection system is now briefly explained. The surveying node, which is a relay node arbitrarily selected from among relay nodes forming a network, is connected to the survey target node, which is another relay node, via a plurality of relay nodes.
Under this network configuration, the surveying node transmits a request message packet including all request messages for requesting a response to the survey target node. On the other hand, when receiving the request message packet from the surveying node, the survey target node generates a response message packet including all response messages, and returns this response message packet to the surveying node.
Here, when not receiving a response message packet from the survey target node, the surveying node determines that a packet discard has occurred between the surveying node and the survey target node. Also, when receiving a response message packet from the survey target node, the surveying node determines that a packet discard has not occurred between the surveying node and the survey target node.
Meanwhile, the detection system has a problem in which a packet discard for each route cannot be detected. That is, the surveying node obtains the same detection result when the request message packet is discarded and when the response message packet is discarded.
Therefore, a network administrator using this detection system detects a packet discard for each route by using the following detecting method.
The surveying node transmits a plurality of request message packets to the survey target node. Every time the surveying node transmits a request message packet, the surveying node adds “1” to the number of transmission of request message packets indicative of the number of request message packets transmitted from the surveying node to the survey target node to count the number of transmission of request message packets.
Also, the surveying node receives a response message packet from the survey target node via a route different from a route via which the request message packet is transmitted. Every time the surveying node receives a response message packet, the surveying node adds “1” to the number of reception of response message packets indicative of the number of response message packets received from the survey target node to count the number of reception of response message packets.
The survey target node receives a request message packet from the surveying node. Every time the survey target node receives a request message packet, the survey target node adds “1” to the number of reception of request message packets indicative of the number of request message packets received by the survey target node from the surveying node to count the number of reception of request message packets.
Also, when receiving a request message packet from the surveying node, the survey target node returns a response message packet to the surveying node via a route different from a route via which the request message packet is received.
Every time the survey target node returns a response message packet, the survey target node adds “1” to the number of transmission of response message packets indicative of the number of response message packets transmitted by the survey target node to the surveying node to count the number of transmission of response message packets.
Then, the network administrator obtains the number of transmission of request message packets and the number of reception of response message packets from the surveying node, and also obtains the number of reception of request message packets and the number of transmission of response message packets from the survey target node.
Subsequently, when the number of transmission of request message packets and the number of reception of request message packets do not match, the network administrator determines that any of the request message packets transmitted from the surveying node to the survey target node has been discarded, detecting a packet discard on the route from the surveying node to the survey target node.
When the number of transmission of response message packets and the number of reception of response message packets do not match, the network administrator determines that any of the response message packets transmitted from the survey target node to the surveying node has been discarded, detecting a packet discard on the route from the survey target node to the surveying node.
The conventional technology explained above is disclosed in, for example, International Publication Pamphlet No. WO2008-117379.
Meanwhile, the detecting method using the conventional detection system disadvantageously forces the network administrator to bear an enormous work cost. For example, the conventional detecting method entails a work cost in which the survey target node has to count the number of reception of request message packets and the number of transmission of response message packets (for example, the survey target node has to install a program for counting the number of reception of request message packets and the number of transmission of response message packets). Moreover, the conventional detecting method entails a work cost of obtaining the number of reception of request message packets and the number of transmission of response message packets from the survey target node. Therefore, the detecting method using the conventional detection system has a problem of forcing the network administrator to bear an enormous work cost.